Jurassic Park Rangers (also known as Jurassic Park security guards) were personnel stationed on Isla Nublar.
They were tasked with maintaining park security and to ensure the safety of the park's visitors. They were also trained to handle a wide variety of other tasks from driving visitors to the visitor's center to shooting down dinosaurs should they pose direct threats to visitors. They would have likely went through training on how to handle a variety of situations and emergencies that might occur during park operations including visitor rescue and treatment of dinosaurs should they fall ill.
While their uniforms in the novel were most likely like police uniforms, the film depicts them having a blue jumpsuit (like one a janitor would wear) with orange helmets sporting the Jurassic Park logo.